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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Neoleptophlebia (Leptophlebiidae) Mayfly Nymph from the Yakima River in Washington
Some characteristics from the microscope images for the tentative species id: The postero-lateral projections are found only on segment 9, not segment 8. Based on the key in Jacobus et al. (2014), it appears to key to Neoleptophlebia adoptiva or Neoleptophlebia heteronea, same as this specimen with pretty different abdominal markings. However, distinguishing between those calls for comparing the lengths of the second and third segment of the labial palp, and this one (like the other one) only seems to have two segments. So I'm stuck on them both. It's likely that the fact that they're immature nymphs stymies identification in some important way.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Stonefly Genus Acroneuria (Golden Stones)

This abundant genus has three important East/Midwest species. The superabundant species in the West have been moved to the new genera Calineuria and Hesperoperla.

Where & when

In 163 records from GBIF, adults of this genus have mostly been collected during June (45%), July (23%), and May (21%).

In 50 records from GBIF, this genus has been collected at elevations ranging from 20 to 10663 ft, with an average (median) of 1721 ft.

Genus Range

Identification

To determine whether a specimen of Perlidae belongs to Acroneuria, use the Key to Genera of Perlidae Nymphs.

Specimens of the Stonefly Genus Acroneuria

1 Female Adult
6 Nymphs

Start a Discussion of Acroneuria

References

Stonefly Genus Acroneuria (Golden Stones)

Taxonomy
10 species (Acroneuria arida, Acroneuria evoluta, Acroneuria filicis, Acroneuria flinti, Acroneuria frisoni, Acroneuria hitchcocki, Acroneuria internata, Acroneuria ozarkensis, Acroneuria perplexa, and Acroneuria petersi) aren't included.
Genus Range
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